The present invention relates generally to the manufacture of crystalline bodies, such as crystalline ingots, and, more particularly, to methods and apparatus for orienting a crystalline body during radiation diffractometry, such as for purposes of initially identifying the location at which an alignment feature, such as a flat or a notch, is to be formed or for thereafter verifying the location of the alignment feature.
The crystalline bodies that are grown, generally in the form of crystalline ingots, during the process of manufacturing semiconductor wafers are crystalline structures. In this regard, the ingots have a predefined crystal orientation in the axial direction, such as an  less than 100 greater than  axial orientation. During a number of subsequent manufacturing operations, the position of the ingot as well as the wafers that are subsequently formed from the ingot with respect to a target plane location, must be precisely determined. For example, other material layers must generally be grown, deposited or otherwise formed upon the wafer in a predetermined manner with respect to the target plane. As known to those skilled in the art, the target plane location is related to the axial orientation in that the relative positional relationship of a family of target planes are defined by the axial orientation. In other words, the axial orientation provides information relating to the angular spacing of a family of target planes, but does not dictate the particular location of any of the target planes. For example, wafers formed from an ingot having an  less than 100 greater than  axial orientation will have a family of four {110} planes separated by 90xc2x0 from one another; any one of which may serve as the target plane.
In order to facilitate proper positioning of the ingot or wafer during subsequent manufacturing operations, an alignment feature, such as a notch or a flat, is typically formed lengthwise along the ingot or more commonly along a block or segment of the ingot (hereinafter collectively referred to as an ingot). By directly identifying the location of the target plane with the alignment feature, subsequent manufacturing operations can be referenced to the alignment feature and, in turn, to the target plane. Alignment features are well known with a flat being typically formed to be parallel to the target plane. In contrast, a notch is typically formed such that a radial line that bisects the notch is perpendicular to the target plane.
In order to form the alignment feature in a desired location, the crystalline body is typically examined to identify the target plane location. Typically, the crystalline body is subjected to radiation, such as x-rays, at a variety of incidence angles. The reflected radiation is monitored and the position of the crystalline body at the time at which the intensity or power of the reflected radiation peaks is noted since the peak power or intensity is indicative of reflections from a crystalline plane, such as the crystalline plane that defines the target plane. Once the crystalline plane that defines the target plane has been identified, the alignment feature can be formed lengthwise along the ingot so as to identify the target plane as described above. Secondary alignment features may also be formed lengthwise along the ingot at other predetermined angular positions with respect to the initial or primary alignment features.
In order to identify the crystalline plane 10 that defines the target plane and, in turn, the proper position of the alignment feature 14, the crystalline body 12 is typically placed upon a stage 16 and is illuminated by a radiation source 18, as shown in FIG. 1. The signals reflected or otherwise returning from the crystalline body are captured by a radiation detector 20. While the crystalline body can be placed in various orientations upon the stage, the crystalline body is typically initially positioned upon the stage based upon habit lines that develop during the growth of the crystalline body and that are consistently located in a known manner with respect to the axial orientation. The crystalline body is then moved upon the stage to alter the angle of incidence of the radiation as the radiation source continues to direct radiation to the crystalline body and the radiation detector continues to detect the reflected radiation. For a substantially cylindrical ingot, for example, the ingot is rotated about its longitudinal axis to vary the angle of incidence. Upon detecting the peak of the reflected radiation, the position of the crystalline plane that defines the target plane is identified and the alignment feature is formed so as to directly identify the target plane. While a variety of devices have been developed for examining a crystalline body to determine the location of a target plane, x-ray diffractometers, such as those sold by Rigaku/USA, Inc. of The Woodlands, Tex., are commonly utilized.
After the alignment feature 14 has been formed, such as by grinding a flat or a notch, the crystalline body 12 is typically re-inspected to verify the position of the alignment feature relative to the target plane since the position of the alignment feature to the target plane is critical during subsequent manufacturing operations. This verification is typically performed by again placing the ingot 12 upon the stage 16 and irradiating the ingot. Based upon the alignment feature, the ingot is positioned upon the stage in such a manner that the crystal plane 10 that defines the target plane of the ingot will reflect the incident radiation, thereby maximizing the power or intensity of the reflected radiation. The radiation reflected or otherwise returning from the ingot is detected while the angle of incidence of the radiation is varied slightly, such as by rotating the stage and the ingot relative to the radiation source 18 and detector 20. By determining the peak of the reflected radiation, the position of the target plane and, in turn, the position of the alignment feature relative to the target plane can be confirmed.
In order to facilitate positioning of the ingot 12 and, in particular, the alignment feature 14 of the ingot relative to the underlying stage 16 and, in turn, to the radiation source 18 and detector 20, a fixture 22 is utilized to engage one end of the ingot and to maintain the ingot in a predefined position relative to the underlying stage. As shown in FIG. 1, a fixture generally includes an upstanding plate 24 having a base 26 for contacting a bar 28 that is mounted to and extends upwardly from the stage. The fixture also includes a pair of supports 30, typically in the form of rollers, carried by the plate for engaging circumferential portions of the crystalline ingot. Additionally, the fixture includes an engagement member 32 threadably connected to the edge of the fixture opposite the base for engaging the alignment feature of the ingot. In this regard, the distal end of the engagement member can include a pin for engaging the bottom portion of a notch. Alternatively, the distal end of the engagement member can be planar for engaging a flat. As shown, a conventional fixture therefore engages the alignment feature of a crystalline ingot such that the alignment feature is positioned opposite the bar with the engagement member extending towards the bar in a perpendicular relationship thereto.
Once the end of the crystalline ingot 12 is engaged by the fixture 22, the ingot is irradiated and the radiation reflected by or otherwise returning from the ingot is detected. The stage 16 is then rotated slightly, such as through an angle of about +/xe2x88x920.5xc2x0, in order to vary the angle of incidence and to determine the position of the crystalline ingot that maximizes the reflected radiation. A conventional fixture, such as shown in FIG. 1, is therefore useful in conjunction with crystalline ingots having an alignment feature 14 that directly identifies the crystal plane 10 that defines the target plane by being in a single predetermined position relative to the crystalline body, i.e., relative to the habit lines extending along the length of the crystalline body. For a crystalline body having a  less than 100 greater than  axial orientation, for example, the conventional fixture may be configured such that, once the crystalline body is mounted within the fixture based upon the habit lines, a {100} plane will be identified and may be utilized as the target plane by directly identifying the {100} target plane with the alignment feature. However, the fixture does not support the identification of other target planes having different positional relationships with respect to the crystalline body. In this regard, some purchasers of semiconductor wafers are specifying that the alignment feature be defined in non-standard locations, thereby altering the positional relationship of the target plane which defines the location of the alignment feature relative to the crystalline body. For example, some purchasers may require that the alignment feature identify a {111} plane of a crystalline body having a  less than 110 greater than  axial orientation.
In order to utilize a conventional fixture, such as the fixture 22 depicted in FIG. 1, to analyze a crystalline body having an alignment feature in a non-standard location, the source of radiation and the radiation detector would have to be modified to irradiate the ingot at a different angle relative to the stage and, in turn, relative to the crystalline body, since the fixture will retain the alignment feature in a position directly opposite the bar even though the alignment feature is now defined in a different positional relationship with respect to the crystalline body. Unfortunately, a conventional x-ray diffractometer is not designed to easily facilitate the disassembly and repositioning of the stage holding the ingot and the radiation detector. As such, any attempts to reconfigure the stage and the radiation detector to irradiate a crystalline ingot at a different angle would be a substantial modification and, even if the modification were possible, the resulting device would have to be requalified and recalibrated to ensure proper measurements were obtained. Additionally, the technicians who conduct the radiation diffractometry analysis are not trained to reconfigure the x-ray diffractometer and, therefore, would require substantial training.
As an alternative to reconfiguring an existing device, an additional x-ray diffractometer could be purchased with the source of radiation and the radiation detector designed to be at the desired angle relative to the stage such that the crystalline body could be properly analyzed to determine if the alignment feature is at the desired non-standard angle with respect to the crystal orientation. Each x-ray diffractometer is quite expensive and generally costs several hundred thousand dollars, thereby rendering it prohibitively expensive to purchase an additional device to analyze ingots for each different non-standard position of the alignment feature.
Depending upon the crystal plane that is to be located, conventional radiation diffractometry techniques may have additional difficulties. In this regard, some crystalline planes are asymmetric. For example, for a crystalline body having a  less than 100 greater than  axial orientation, two {100} planes are defined at 0xc2x0 and 180xc2x0 and two {110} planes are defined at 90xc2x0 and 270xc2x0. In contrast, the  less than 211 greater than  orientation is asymmetric and defines crystal planes at +/xe2x88x9254.7xc2x0 and +/125.3xc2x0 as shown in FIG. 2. As such, two pairs of  less than 211 greater than  crystal planes exist, namely, a first pair at +54.7xc2x0 and xe2x88x92125.3xc2x0 and a second pair at xe2x88x9254.7xc2x0 and +125.3xc2x0. In instances in which the alignment feature is to identify a specific pair of the  less than 211 greater than  crystal planes, the direct identification of the desired pair of  less than 211 greater than  crystal planes is generally unworkable since a technician will be unable to determine which pair of  less than 211 greater than  crystal planes was identified by merely examining the peak of the returned radiation over the relatively small range of incidence angles supported by the rotation of the stage.
Still further, the radiation that is reflected and is collected by a radiation detector not only has a primary peak 34 that signifies reflections from the desired crystal plane, but may have a minor or secondary peak 36 at a different wavelength caused by K-alpha II radiation as shown in FIG. 3. As such, some technicians may inadvertently identify the secondary peak as the peak representative of the reflections from the crystal plane of interest and, therefore, improperly determine the location of the crystal plane of interest. The angle or separation between the primary and secondary peaks depends on, among other things, the position of the source of radiation and the radiation detector. In this regard, increases in the angle, termed theta xcex8 as shown in FIG. 1, between the source of radiation and the crystalline plane of interest and, in turn, between the crystalline plane of interest and the radiation detector also increases the angle or separation between the primary and secondary peaks. Thus, the identification of crystal planes having a relatively large angle with respect to the source of radiation and, in turn, with respect to the radiation detector may render it difficult to reliably identify the primary peak of the detected radiation, thereby complicating the identification of the crystal plane of interest.
As such, it would be desirable to develop a more reliable technique for identifying crystal planes within a crystalline body, such as an ingot. In addition, it would be desirable to develop a technique for identifying the crystal plane that defines the target plane of a crystalline body in instances in which the alignment feature is at any of a variety of non-standard positions without modifying existing x-ray diffractometers and without purchasing additional x-ray diffractometers.
A method and apparatus are therefore provided for orienting a crystalline body during radiation diffractometry which addresses the foregoing drawbacks associated with conventional techniques. In particular, the method and apparatus of the present invention facilitate orientation of a crystalline body even in instances in which the alignment feature is defined at various non-standard angles with respect to the crystalline body. Moreover, the method and apparatus of the present invention can utilize conventional x-ray diffractometry equipment and thereby eliminate any need to alter existing x-ray diffractometry equipment or to purchase additional x-ray diffractometry equipment. Additionally, the method and apparatus of one advantageous aspect of the present invention facilitate the indirect identification of a target plane based upon the identification of a reference plane which is offset by a predetermined angle from the target plane of interest, but which reflects radiation having a more clearly distinguishable peak than the target plane and/or can be utilized to identify a specific pair of crystal planes from among a plurality of asymmetric crystal planes in an unambiguous manner.
According to one embodiment, an improved method and apparatus for orienting a crystalline body during radiation diffractometry are provided. The apparatus includes a frame having a first member adapted to support the frame relative to a source of radiation and a second member moveably connected to the first member. The frame also includes an engagement member carried by the second member for engaging a predetermined portion of the crystalline body, such as an alignment feature of the crystalline body, to thereby define the angle at which the incident radiation will impinge upon the crystalline body. Thus, the second member of the frame can be positioned relative to the first member of the frame based upon a predefined angular offset between a reference plane to be located based upon the reflected radiation and a target plane identified by the alignment feature of a crystalline body.
The first member can include a base for supporting the frame relative to the source of radiation, such as by contacting a bar connected to and extending outwardly from the stage of an x-ray diffractometer. A second member may also define an aperture for viewing the engagement of the predetermined portions of the crystalline body, such as the alignment feature of the crystalline body, by the engagement member. Additionally, the engagement member may be threadably connected to the second member so as to be threadably advanced into contact with the predetermined portion, such as the alignment feature, of the crystalline body. The frame of this embodiment can also include a third member for locking the first and second members in position with respect to one another. Each of the first and second members may include indicia to facilitate positioning of the first and second members relative to one another. A second member may also include at least one support for engaging another portion of the crystalline body.
The apparatus and associated method of this embodiment facilitate an analysis of the position of an alignment feature relative to the crystalline body, even in instances in which the alignment feature is disposed at various non-standard positions. In this regard, the alignment feature of the crystalline body can be angularly offset from the crystal plane, i.e., the reference plane, that the x-ray diffractometer is designed to detect. By adjusting the angular position of the second member relative to the first member, the apparatus and method of this embodiment can accommodate different angular offsets between the orientation feature and the crystal plane detected during x-ray diffractometry.
According to another aspect of the present invention, an apparatus for orienting the crystalline body during radiation diffractometry includes a frame for supporting at least a portion of the crystalline body and including a base adapted to support the frame relative to a source of radiation. For example, the base may contact a bar connected to and extending outwardly from the stage of an x-ray diffractometer or the like. The apparatus also includes an engagement member carried by the frame for engaging a predetermined portion of the crystalline body, such as the alignment feature of the crystalline body. According to this aspect of the present invention, the engagement member extends at a non-orthogonal angle relative to the base.
The frame may have a number of different configurations, depending upon the angular offset between the reference plane to be detected from the reflected radiation and the target plane to be identified. In one embodiment, the frame includes a central portion and at least two arms extending outwardly from the central portion. One of the arms is connected to the base and another of the arms carries the engagement member. The frame may also include a central portion and the first, second and third arms extending outwardly from the central portion. In this embodiment, the first arm is connected to the base and the third arm carries the engagement member. The third arm also defines an axis extending through the central portion and bisecting the angle defined between the first and second arms. While at least one arm may be movable with respect to the remainder of the frame, the arms may be fixed at a predefined angle to accommodate instances in which the alignment feature is repeatedly formed at the same non-standard angle. For example, the arms may be positioned such that the engagement member extends at an angle of 45xc2x0 with respect to the base. This exemplary embodiment is particularly useful in instances in which a crystalline body having a  less than 100 greater than  axial orientation has an alignment feature that defines a {100} crystal plane since the {110} crystal plane and the {111} crystal plane that a conventional x-ray diffractometer is designed to detect are offset by 45xc2x0.
According to another aspect of the present invention, a method is provided for indirectly identifying a target plane defined by a crystalline body. For example, the target plane may be the plane defined by the alignment feature of the crystalline body such that the indirect identification of the target plane serves to verify the location of the alignment feature. Alternatively, the indirect identification of the target plane may also identify the location at which the initial or primary alignment feature is to be formed.
According to this aspect, radiation returning from the crystalline body is analyzed to identify a reference plane defined by the crystalline body. Once the reference plane has been identified, the target plane is located based upon a predefined angular offset between the reference plane and the target plane. Thus, the target plane may be indirectly detected by directly detecting the reference plane and then adding or subtracting the predefined angular offset between the reference plane and the target plane. In instances in which the location of an alignment feature is to be verified, the positional relationship of the target plane to the alignment feature may be determined. For example, it may be determined that the alignment feature is properly located if the angular offset between the target plane and the alignment feature is less than a predetermined threshold. Alternatively, in instances in which an initial or primary alignment feature is to be formed, the alignment feature may be formed so as to identify the target plane.
Typically, the crystalline body is irradiated and the radiation that returns from the crystalline body is detected in order to identify the reference plane defined by the crystalline body. In this regard, the radiation that impinges upon the crystalline body is typically directed toward the crystalline body at a plurality of incidence angles. As such, the reference plane may be identified based upon the incidence angle of the radiation at which the radiation having the greatest power is reflected and, in turn, detected.
By indirectly detecting a target plane based upon the detection of a reference plane and the predefined angular offset between the reference plane and the target plane, the method of this aspect to the present invention facilitates the indirect identification of the plane identified by the alignment feature based upon the direct identification of the reference plane, typically the crystal plane that an x-ray diffractometer is adapted to detect without any reconfiguration. Moreover, the method of this aspect of the present invention may facilitate the identification of a target plane in a more reliable manner than attempts to directly identify the target plane since, in some circumstances, the reference plane will reflect radiation having a more clearly distinguishable peak than the target plane that may otherwise reflect radiation in such a manner as to generate a deceptively large secondary peak. Moreover, a target plane that belongs to a family of asymmetric planes may be specifically determined by identifying a reference plane having a predetermined relationship with the target plane, thereby permitting the unambiguous identification of the target plane relative to the other planes in a family of asymmetric planes. Thus, the method and apparatus of the various embodiments of the present invention address the drawbacks identified by prior radiation diffractometry techniques and provide an improved technique for identifying a target plane, such as the crystal plane identified by an alignment feature.